During the development of many machines, the use of fluids is an integral part of the operation of the machine. For example, many machines rely upon a power source and a transmission system to provide controlled application of power. Transmissions can be a set of cooperating gears for speed and torque conversions from a power source (such as a rotating power source) to another device (such as a drive axle or propeller). In operation, the transmission uses transmission fluid to provide hydraulic power to move the gears from one location to another to perform the power redirection, and speed and torque conversions.
One of the operational realities with transmission fluid is that transmissions can create a high temperature environment. The internal friction can increase the operational temperature to over 250° F., significantly above the normal operating temperature of about 175° F. At temperatures higher than the normal operating temperature, the transmission fluid can oxidize which can destroy the lubricating properties and can result in contaminates entering the fluid stream. High operating temperatures cause seals to breakdown which can result in dirt and other contaminates entering the fluid. Further, the normal operation can cause contaminates to become present in the fluid.
Transmission filters are used to help remove these contaminants from the transmission fluid itself. The filter can hold metal particles, debris and other foreign material to prevent the material from continued circulation in the fluid stream. Characteristics of filter media include the ability to remove a certain percentage of particulate of a certain size, durability, porosity, high temperature operations and the like. It can be desirable to have various layers of filter material which operate to provide certain physical characteristic. Further, multiple layers can provide for mechanical stability of the filter medium itself.
There are several types of filter media that have been previously attempted for use with hydraulic fluid filtration, and include air-laid and wet-laid processing which can provide filtration for both air and fluid streams. However, most of these materials, especially non-woven material, can suffer from a lack of mechanical strength and shortened operational life when in contact with a fluid, including transmission fluids. Further, pressures from the fluid stream can exceed the burst threshold of these materials rendering the medium useless in such environments if the filter material has a structural failure (e.g. bursts).
There have been several attempts to produce a non-woven filter media with sufficient physical properties to be used in filter media. For example, U.S. Pat. No. 6,695,148 is directed to a transmission fluid filter felt. However, these attempts fail to provide a filter media with sufficient particulate removal, strength and filtration life using a layered arrangement of materials with different densities to provide the desired filtering characteristics. Additional attempts to provide for a high strength, high capacity filter media include U.S. Pat. Nos. 4,161,422; 4,274,914; 4,713,285; 4,765,812; 5,068,141 and 5,283,106.
It would be advantageous for the manufacturing of hydraulic filters to have a filter media that was a high strength, high capacity filter without the limitations existing in the prior art such as lack of burst strength when used in wet, high pressure fluid streams and air streams.
Therefore, it is an object of the current invention to provide a high strength filter medium that can be used in the filtration of fluids capable of operating in a high pressure, high temperature environment.
It is another object of the present invention to provide for a layered filter material for use in a filter medium having different fiber types carried by a scrim to provide mechanical support for the filter material.